Metallized polymer compositions, processes for their preparation and their uses

ABSTRACT

Metallized polymer compositions are disclosed, the surface of which comprises an intermetallic compound of a metal element A (Sn, As, Sb or Bi) and a metal element B (Fe, Co, Ni, Cu, Zn, Ga, Ru, Rh, Pd, Ag, Cd or In), preferably an intermetallic compound of antimony and a metal element B. Processes for producing such metallized polymer compositions involve either the reduction of a metal element A compound in the presence of metallic metal element B and the polymer or the compression of a laminate of metal element A and metal element B layers onto the polymer. The metallized polymers are useful in the production of printing circuit boards, electromagnetic interference shielding devices, membrane switches, capacitors, conductive fibers, magnetic tapes and disc, antistatic mats, barrier polymers and optical storage devices.

BACKGROUND OF THE INVENTION

The present invention relates to polymer compositions which aremetallized, in particular with intermetallic compounds. The inventionalso relates to convenient processes for preparing such metallizedpolymer compositions. Furthermore, the invention relates to a processfor producing electrically conductive films. Finally, the inventionenvisages advantageous uses of the processes.

In the development of currently available commercial processes ofproducing satisfactory metal-to-plastic bonding the plating of polymericmaterials has met increasing interest and found widening applications.The replacement for metal articles by plastic items obviously offers theadvantages of lower cost, higher production speed, wider designlatitude, weight savings and fewer corrosion problems in view of theapplicable extrusion and injection molding techniques, and the inherentproperties of the polymeric materials. For many application purposes,however, a metallic coating on the polymeric article is desirable, sincein that way the hardness, wear resistance, shiny appearance and metallicfeel characteristic of metals is imparted to the polymeric substitutes.Furthermore, mention should be made of printed circuit boards whichcomprise dielectric substrates carrying metal electrical circuits.Finally the plating of plastic articles has found application inshielding electromagnetic interference (EMI) from electronic equipment.This EMI causes problems to advanced electronic devices of greatsensitivity. Regulations concerning this new electronic pollution are orwill be effective in USA and Europe.

Since most plastic surfaces are not electrically conductive, thetraditional electroplating methods are not quite suitable for providinga metallic coating. Currently, however, electroless plating is onefeasible method for the plating of polymeric materials. Though thedevelopment of chemical etchants resulting in a controlled microporoussurface of the polymeric material and greatly improved electrolessplating baths has led to metal depositions which adhere well to thepolymeric surface and may serve as a conductive preplating forsubsequent electroplating, all electroless plating processes are laborintensive, complicated and hence expensive. For example, a typicalelectroless plating procedure involves the steps of etching thepolymeric material with strongly oxidizing solutions of chromic acid inorder to physically roughen the polymeric surface and chemically modifyit to give it a hydrophilic nature, neutralizing it with a mildly acidicor basic reducing agent for removing the detrimental hexavalentchromium, sensitizing it with stannous chloride and palladium chloridefor nucleation of palladium, accelerating it with acidic or basicsolutions for removing excess tin and exposing pallidium nuclei andelectroless depositing metals such as nickel and copper on it from aplating bath.

A method for high-speed production of metal-clad articles is disclosedin the International Patent Application No. WO 02784, which methodcomprises electroplating the injection molding die surface prior to eachmolding operation of a plastic article and the transfer of theelectrodeposit to the plastic surface as a result of the higher adhesionof the electrodeposit to the plastic article formed than to the surfaceof the mold member. This method, however, requires the preliminaryformation of the metallic layer and subsequent bonding to the polymericarticle during formation of the latter.

Further, it is known from GB Patent No. 1,309,320 that flammableplastics can be compounded with combinations of halogen containing lowmolecular weight compounds and antimony trioxide. It is stated thereinthat certain additives tend to effloresce through lack of compatibilitywith the plastics material, which over a period of time, can result inthick coatings being formed on the surfaces of molding or machine parts.The nature of such coatings, however, is not defined, and no use ismentioned.

From EP Patent Application No. 125,617 it is known to metallize polymercompositions by heat treatment of a composition of a polymer and anorganic complex of a transition metal element. A metallized surface filmwas obtained when the heat treatment was conducted with the polymercomposition being in initimate contact with a metallizing board, whichhad to be made of a material having adequate heat resistance and to bereadily releasable from the metallized film. The metal layers obtaineddid not contain a main group element.

In U.S. Pat. No. 3,620,834 a method is disclosed for metal platingplastic materials, wherein a substrate is successively pretreated with amain group V element trichloride and a source of sulfide prior toelectrodeposition of Ni or Cu by conventional techniques.

From German Patent Application No. 2,022,109 it is known to treat in thepresence of a solvent the surface of a plastic article with a dissolvedmetal salt complex, such as SnC1₂. DMSO, which diffuses into theplastics material during treatment and is anchored therein. The surfacetreated may be sensitized with a different metal salt, such as AgNo₃,under reducing conditions, so that a metallic layer of the latter metalis deposited. The treatment bath must be renewed as it is depleted andthe silver tends to plate on the process equipment, causing a veryuntidy condition.

U.S. Pat. No. 4,459,330 discloses a wet process for plating a main groupmetal on aromatic polymers by the use of a non-aqueous solution of asalt of an alkali metal in a positive valency state and a main groupmetal in a negative valency state, for example K₄ Sn₉. Metal plating isaccomplished by immersion of the polymer into the solution followed bywashing with toluene.

An article in The Journal of Vacuum Science and Technology, Vol. 9, No.1, pp. 354-6 describes the preparation of intermetallic compounds,specifically of niobium and tin, Nb₃ Sn, by coevaporation of two metalsonto a rotating surface. A plurality of successive thin layers each ofthe thickness of approximately one lattice constant should be depositedfor properly producing the intermetallic compound, which finally iscollected from the carrying surface.

Other current techniques, such as vacuum metallizing and cathodesputtering, are available (Modern Plastics Encyclopedia 1983-1984, p.358-374), but are not always useful.

In view of the increasing need for plated polymeric articles it will beclear that there is still a great demand for such a simple methodproviding an adhering interface between a polymeric material and ametallic or psuedo-metallic layer, that will be less cumbersome andcomplicated than the prior art methods discussed above.

The present invention thus has for its primary objectives the providingof a relatively simple method for metallizing polymeric materials aswell as the obtaining of a novel metallized polymer composition.

SUMMARY OF THE INVENTION

Accordingly, the present invention, in the first embodiment, comprises ametallized polymer composition, of which the surface is at leastpartially metallized with a surface layer comprising an intermetalliccombination containing a metal element A selected from the groupconsisting of tin, arsenic, antimony and bismuth and a metal element Bselected from the group consisting of iron, cobalt, nickel, copper,zinc, gallium, ruthenium, rhodium, palladium, silver, cadmiun andindium.

In a second embodiment, the present invention comprises a process forpreparing a metallized polymer composition comprising reacting acompound or mixture of compounds containing a positively valent metalelement A selected from the group consisting of tin, arsenic, antimonyand bismuth with a metallic source of a metal element B selected fromthe group consisting of iron, cobalt, nickel, copper, zinc, gallium,ruthenium, rhodium, palladium, silver, cadmium, and indium. The reactionis effected at the surface of the polymer composition under metallizingconditions such that a surface layer is formed on the polymercomposition comprising a intermetallic combination containing both themetal element A and the metal element B.

In a third embodiment, the present invention comprises a process forpreparing a metallized polymer composition. The process comprisesbringing into contact at least one layer of zero-valent antimony and atleast one layer of a metal element B selected from the group consistingof iron, cobalt, nickel, copper, zinc, gallium, ruthenium, rhodium,palladium, silver, cadmium and indium with a polymer or prepolymercomposition under metallizing conditions such that a polymer compositionis formed having a surface layer comprising an intermetallic compound ofantimony and the metal element B.

In a fourth embodiment the present invention comprises a process forpreparing electrically conductive films. The process comprises the stepsof incorporating a compound or mixture of compounds containing a metalelement A selected from the group consisting of tin, arsenic, antimonyand bismuth and metallic particles comprising a metal element B selectedfrom the group consisting of tin, arsenic, antimony and bismuth andmetallic particles comprising a metal element B selected from the groupconsisting of iron, cobalt, nickel, copper, zinc, gallium, ruthenium,rhodium, palladium, silver, cadmiium and indium into a thermosettingpolymer composition to obtain a paste. The paste is spread to form afilm. The film is subjected to heating in such a manner that thethermosetting material is cured and the particles of metal element Areact with the particles of metal element B to form surface layers onthe internal surfaces of the thermosetting material which envelope theparticles of metal element B. The surface layers comprise anintermetallic combination containing both the metal element A and themetal element B and are interconnected throughout the polymer matrix.

Other embodiments of the present invention encompass details about howthe components of the invention are brought together, metallizingreaction conditions and compositions of the various components all ofwhich are hereinafter disclosed in the following discussion of each ofthe facets of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The metallic surface layer of the present metallized polymercompositions contains in an intermetallic combination at least two metalelements selected from each of the groups A and B defined above.Specific intermetallic compounds are Cu₂ Sb, FeSb₂, SbZn, Sb₃ Zn₄ andInSb. Such intermetallic surface layers appear to adhere well to thevarious polymer compositions. They are electrically conductive to anextent which depends upon the nature of the intermetallic compound andthe thickness of the layer. For many of the applications mentionedearlier the electric conductively is sufficiently high and the presentmetallized polymer materials are useful as such. If desired, theintermetallic surface layers may be plated with any further metal ormetal combination, which is effected most conveniently byelectrodeposition in that the surface has become electricallyconductive.

The term "intermetallic combination" as used herein is intended toinclude what are understood to be intermetallic compounds, such as Cu₂Sb, as well as metal alloys. There is some controversy in the literatureas to the formal valency of the metal atom components of intermetalliccompounds, the prevailing opinion being that all metal atoms in suchcompounds are zero-valent, although actually carrying a minimal charge.

The present metallized polymer compositions can be readily produced bytechniques which are basically either of a chemical or of a physicalnature. In the preferred process embodiments of the present inventionsuch chemical or physical processes are effected when at elevatedtemperature and at elevated pressure the metallic precursors are incontact with the surface of the (pre) polymer composition to bemetallized, so that the latter is in the thermoplastic state or issubject to a thermosetting reaction. It is believed that the excellentadhesion is at least partially due to such a contact during theformation of the intermetallic combination.

The processes of the present invention are thus in markedcontradistinction to the above prior art which teaches metallization ofpolymer compositions only by the most complicated and difficultprocedures. Such procedures involve wet processes, includingelectrodeposition, or electroless plating or provide no teaching of theobtaining of intermetallic surface layers on a polymer. The presentinvention is at least partially based on the surprising discovery thatin the formation of an intermetallic combination at a polymer surface bythe relatively simple methods of the present invention, the strongadhesion which occurs between the combination and polymer is at least asstrong as the adhesions obtained by the prior art processes between ametal coating and polymer surface.

The compositions of the present invention comprising particularintermetallic combinations on a polymer surface are not known to the artand there does not appear to be any way the could be made by the knownprocesses. In particular, electroless deposition baths are chemicallyreactive metastable solutions which upon contact with catalyticnucleation centers spontaneously deposit the Cu or Ni metal from thebaths. It is not conceivable that mixed baths could be employed toobtain the composition of the present invention. There is no reason tobelieve that the tin (IV) ions which stablize and effect bonding of thepalladium catalyst to the polymer prior to the electroless plating stepare to any extent reduced to zero valance in the course of the platingso as to form even the smallest amount of intermetallic combination.

In the broadest embodiment of the chemical process of the inventionwhich employs a compound or mixture of compounds containing the metalelement A such compound and the source of a metal element B are simplybrought together to be reacted on the surface of the polymer compositionto be metallized. Reaction products containing metal elements A and Bwill be deposited to form a surface layer on the polymer composition. Ifnecessary, reaction may subsequently be initiated by elevatingtemperature and/or pressure. Usually the invention will employ, in thisembodiment which involves a chemical process, a stoicheometric excess ofelement B. In the course of the reaction a portion of metal element Bwill replace element A in the compound or compounds while a furtherportion of element B will join with element A in the intermetalliccombination. Metal element A is selected from the group consisting oftin, arsenic, antimony and bismuth, while metal element B is selectedfrom the group consisting of iron, cobalt, nickel, copper, zinc,gallium, ruthenium, rhodium, palladium, silver, cadmium and indium. Asurface layer will be formed on the polymer composition containing boththe element A and the metal element B.

It is the combination of a metal element A with a metal element B thatis critical to the present invention. A combination of two group Ametals or two groups B metals could not be applied as a metallic coatingby the chemical and physical processes of the invention, because thechemical reactions and diffusion phenomena on which the invention reliesdo not occur between such combinations.

The source of metal element B may be of a pure metal element B, but mayalso be of an alloy thereof. But the metal element B will be containedin its zero valency state. Preferably the metal element B is chosen fromthe group consisting of nickel, copper, zinc and indium. Within thisgroup copper is especially preferred. When copper is selected as themetal element B, the surface layer obtained has been proven to be anexcellent base for further electrodeposition.

The chemical process embodiment of the invention may employ a metallicsurface which functions both as a source of a metal element B and as asupport surface. The support surface may be the metallic surface of abulk body of homogeneous composition, or a metallic coating on a body ofany other composition such as foil of metal B placed on the surface of astandard mold. The polymer composition is pressed on to this metallicsurface in the presence of the metal element A compound, which maypreviously have been applied to either surface or to both surfaces ofthe polymeric and metallic materials by common procedures such asspraying, dusting or brushing.

The compound or mixture of compounds containing the metal element A maybe incorporated into the polymer composition before the latter ispressed onto a metallic surface containing the metal element B. Thisembodiment may be preferred, if the contact face is of irregular shapeand the contacting is to be combined with a molding operation of thepolymer composition. Under suitable process conditions the compound ormixture of compounds, or further products formed thereof will prove tobe sufficiently mobile in the polymeric mass to reach the surface of thepolymer mass within the applied time parameter, so that a thick surfacelayer relative to the concentration in the bulk of the polymercomposition can be formed.

Effective compositions may further contain suitable inert excipients.

Of course, the basic features of the above embodiments may be combinedwithin the scope of the invention. For example a metallic surfacecontaining a metal element B may be used, and further metallic particlescontaining a metal element B may be provided between the metallicsurface and the polymer composition together with the metal element Acompound. In that case the metallic surface and the metallic particlesmay contain different metal elements B.

The essential reactions of the compound or mixture of compoundscontaining the metal element A may take place at the surface of metalelement B metallic particles surrounded by the polymer composition. Inthat case the metallic particle will remain enveloped within a polymericlayer containing on its internal surface the deposited combination ofthe metal elements A and B which is formed in the process of theinvention. Since this layer appears to be in electrically conductivecontact with the metallic particle contained therein, its formationaccording to the invention may be used in the production of electricallyconductive films.

The process for producing the electrically conductive films comprisesthe steps of incorporating a compound or mixture of compounds containinga metal element A and metallic particles containing a metal element Binto a thermosetting polymer composition to obtain a paste, spreadingthe paste to form a film, subjecting the film to heating in such amanner that the thermosetting material is cured and the metal element Ais brought into reaction with the metallic particles. This results inthe formation of a network of polymeric envelopes containing individualmetallic particles with the internal surface of the envelopes having asurface layer comprising an intermetallic combination containing themetal element A and the metal element B. These internal surfaces withtheir metallic surface layer are interconnected throughout the polymermatrix, thus rendering the film conductive.

The thickeness of the conductive film made from the above paste mayrange from about 10 to about 1000 microns. The curing temperature mayrange from ambient to about 250° C., preferably about 50° to about 125°C. The components in the paste mixture may comprise from about 20 toabout 70 wt. % of metal element B finely divided (0.1-20 micronsdiameter) particles (such as Cu), about 20 to about 70 wt. % of curablebinder (such as urethane) and about 5 to about 40 wt. % of finelydivided particles of metal element A compound (such as SbC1₃). The pastemay optionally contain 0-200 wt. %, based on the total weight of theabove components, of a volatile diluent (such as butanone).

The expression "metal element", as used in the present specification andclaims, is meant to encompass both metal elements and semi-metalelements, since no sharp division between them can be made. "Polymercomposition" is any composition containing a polymer or copolymer asmain constituent together with any additives being inert in the presentprocess. The (co)polymers may be thermoplastic or thermosetting.

In the chemical process according to the invention use is made of acompound or mixture of compounds containing a metal element A which willbe in a positive valency state. Of course, in the surface layer formingstage of the process at least one reactive compound must be present, butsuch a reactive compound may very well be formed in situ, in which casea mixture of compounds is used comprising precursors for the reactivecompounds. Such precursors will in general comprise an inactive or lessreactive source of the metal element A as first constituent and anactivating compound as second constituent. The use of precursors may bepreferred in view of the availability of starting materials and most ofall when an induction time, induction temperature or induction pressureare desirable, for initiating the surface layer forming reaction ratherthan the reaction occuring spontaneously as soon as the reactants arebrought together.

In its broadest scope the invention comprises the formation of surfacelayers containing a metal element A selected from the group tin,arsenic, antimony and bismuth. In order to obtain mixed surface layersit is of course within the scope of the invention to use reactivecompositions containing more than one of these metal elements Aindicated. Reactive compounds of the metal element A comprise, forexample, hydrides, halides, phosphides, sulfides, nitrates, carboxylatesand tartrates and mixed compounds of the metal elements mentioned above.Examples are halides, such as stannous chloride, antimony trichloride,bismuth trichloride, bismuth pentabromide, antimony chloro dibromide,bismuth difluoro chloride, phosphides such as tin phosphides, sulfidessuch as arsenic sulfide, antimony sulfide, hydrides, and mixed compoundssuch as antimony iodo sulfide, and bismuth oxyfluoride.

Other sources of the metal element A usable in the process of theinvention, which may be less reactive or inactive and which preferablyare used as precursors in combination with an activating compound,include oxides, some sulfides, nitrides, salts of mineral acids,amphoteric oxides and salts of amphoteric elements, and carbonates ofthe metal elements mentioned before. Also included are complexes orchelates of these metals and organo metal derivatives. Specific examplesare arsenic oxide, bismuth oxide, tin oxides, etc.

Examples of compounds of anitmony, a preferred metal element A, includeantimony oxides, nitrates, oxyhalides, stearates and mercaptoacetates,organo-antimony compounds, and organic chelates of antimony.

When a precursor to a reactive compound of the metal element A isemployed, a second constituent is required, which will provide thehalogen, sulfur, phosphorous, hydrogen, nitrate, carboxylate or tartrategroup for formation of the reactive compounds. As the halides ofantimony, bismuth and tin are the preferred compounds for use in theprocess of the invention, the second constituent of the precursorspreferably comprises a halogen source, which may contain the halogenboth as a radical and as an ion. The halogen source may comprise organicchloro, bormo, fluoro and iodo compounds as well as inorganic chloro,bromo, fluoro and iodo compounds including organo metallic halides. Thehalogen source may be a halogen containing polymeric component of thepolymer composition.

To produce a metallized polymer composition, the invention provides asecond process, which is basically of a physical nature, in whichprocess at least one layer of zero-valent antimony together with atleast one layer of a metal element B selected from the group consistingof iron, cobalt, nickel, copper, zinc, gallium, ruthenium, rhodium,palladium, silver, cadimium and indium are brought into contact with apolymer or prepolymer composition under conditions such that a polymercomposition is formed having a surface layer comprising an intermetalliccompound of antimony and the metal element B. So, for example, it hasbeen observed that when subjecting a laminate of a copper foil, anintermediate relatively thin layer of antimony and a plastics sheet,such as an ABS-sheet, to heat and pressure the antimony diffuses intothe copper surface layer with formation of the Cu₂ Sb intermetalaliccompound. After cooling the bond between the ABS-sheet and theintermediate Cu₂ Sb layer appears to be stronger than the bond betweenthe Cu₂ Sb layer and the remainder of the copper foil. When theABS-sheet is separated from the copper foil, together with the antimonydiffused therein is transferred to the ABS-sheet in the form of awell-adhering intermetallic compound coating.

In the physical process of the invention both the antimony and the metalelement B are provided as zero-valent starting materials in separatelayers. The layers are provided on top of each other and then togetherthey are pressed onto the polymer composition, preferably at elevatedtemperature. The polymer composition may be in direct contact witheither an antimony or a metal element B layer.

Conveniently, a layer of antimony is deposited upon a metal element Blayer, which in itself may be layer deposited on an inert releasesubstrate, in which case the total matter if the two deposited layers inthe form of a single intermetallic compound layer is transferred fromthe release substrate to the polymer composition surface. Alternatively,the metal element B layer is constituted by the surface layer of a bulkbody consisting essentially of the metal element B, in which case a thinsurface layer thereof is combined with the antimony to form theintermetallic compound and transferred to the polymer compositionsurface.

In one embodiment of the physical process of the invention a layer ofantimony is deposited, for example electrodeposited, onto a foil of themetal element B, whereupon the coated foil is pressed onto a polymercomposition and the assembly is kept at an elevated temperature for asufficiently long time to complete formation of the intermetalliccompound. After cooling the polymer composition carrying at its contactsurface a layer of the intermetallic compound is separated from thefoil, which after cleaning, if desired, may be used in a next cycle.Since in each cycle some of the metal element B is removed from thefoil, it can only be used in a limited number of cycles. An advantage ofthis embodiment, however, is the fact that the thicknesses of thestarting layers are not critical, since the formation of theintermetallic compound will just consume the stoechiometrically requiredamount relative to the amount of antimony deposited.

According to another embodiment of the physical process of the inventionan inert release substrate, for example an endless belt, is provided, onwhich a layer of antimony and a layer of the metal element B areconsecutively deposited, for example by electrodeposition, in eithersequence. Any desired number of layers may be deposited in asandwich-like arrangement.

Thereupon, the inert substrate carrying the combined depositions ispressed onto a polymer composition, which for example is in the form ofan endless foil, at elevated temperature. The deposited layers ofantimony and the metal element B may be preheated for a certain time inorder to avoid too long residence times of the polymer composition inthe heated contact step. Finally, the polymer composition coated withthe intermetallic compound may be separated from the inert releasesubstrate. This second embodiment may advantageously be carried out in acontinuous mode.

The combined layers of antimony and the metal element B may also bebrought into contact with a prepolymer composition comprising precursorsof the final polymer. For example, such precursors may be charged uponan endless belt previously coated with antimony and metal element Blayers, whereupon the assembly is heated and pressurized, inducing boththe intermetallic compound formation and the polymerization.

Although electrodeposition is preferred, any other known method fordepositing a metal layer upon a substrate, such as electrolessdeposition, vacuum metallizing, and cathode sputtering may be used toprepare the assembly of layers of antimony and the metal element Brespectively.

The process conditions of both the chemical and the physical process ofthe invention may in principle by widely varied. The process temperaturewill be limited by the degree of heat stability of the polymericmaterial used. Low temperatures should be avoided if they lead tolengthy reaction times. Preferably the processes of the invention arecarried out at a temperature in the range of from ambient to 600° C.,whereas a range of from 125° C. to 375° is particularly preferred, and arange of from 200° C. to 250° is most preferred.

In principle any pressure may be used in the processes of the invention.In many cases, however, better contacting will be achieved at elevatedpressures. Preferably the pressure ranges from 100 kPa to 100 MPa absand most preferably from 100 kPa to 10 MPa. Temperatures and pressuresfor a given system of metal A or metal A compounds, metal B andpolymeric material, which are appropriate for obtaining theintermetallic compound of metals A and B that adheres to the polymersurface, referred to herein as "metallizing conditions", can easily bedetermined empirically for any given case by one of ordinary skill inthe art without undue experimentation.

The polymer composition used in the process of the invention comprisespolymers such as thermoplastics, thermosets, thermoplastic rubbers,elastomers and their blends. Examples of suitable polymers arepolyolefins, polystyrenes, polyvinyl halides, polycarbonates,polyesters, polyamides, polyimides, polyetherimides, polysulfones,polyethersulfones, polyetheretherketone, polyacrylonitrile,polychoroprene, polyphenylene oxide, fluoropolymers, silicones,cellulosics, chlorosulphonated polyethylene, nitrilebutadiene rubbers,polyurethyanes, phenolformaldehyde resins, melamine formaldehyde resinsand urea formaldehyde resins and copolymers thereof. Of specialadvantage is the use of copolymers of acrylonitrile, butadiene andstyrene. Especially important are fire retardant grades of polymers.

Further examples of suitable (co)polymers include polypropylene oxide,polypropylene sulfide, polyacrylates, polyalkylacrylates, polysulfidepolymers, polythiazoles, polyethers, polythioethers, polyureas,polyvinyl acetates, polyvinyl alcohol, polyvinyl butyral, polyvinylcarbazole, polyvinyl fluoride, poly(p-phenylene), polyacetates,polyacreolein, polyacrylic acid, phenolics, epoxy resins, andethoxylated bisphenol-A-dimethacrylates.

The polymer compositions used may comprise the above polymers incombination with common fillers, diluents, reinforcing agents, extendersand similar additives, such as stabilizers, antioxidants, pigments, etc.The additives may include quaternary ammonium salts for increasing thepolarity of the polymer composition, which may in some case improve theadhesion to the polymer surface and/or the mobility of the reactivecompounds containing the metal element A in the plastic polymeric massduring contacting.

In the processes according to the invention, the metallization iseffected at temperatures and pressures as indicated above during periodsof time ranging from a few seconds to a number of minutes or severalhours, depending on the thickness of the surface layer desired and theprocess parameters. The polymer composition may be premolded and simplyplaced on contact with a metallic surface of similar shape. Optionallythe polymer composition is pressed against the the metallic surface.Preheating to the desired process temperature may be effected prior tocontacting, but alternatively the assembly of metallic surface andpolymeric material may be pressed together first and subsequently beheated.

If partial coating of the polymeric molding is desired, the polymericmolding may be contacted with a partially embossed surface or thecomposition containing the metal element A may be present inpre-determined contact face areas.

According to the invention contacting also may be effected during themolding of a polymeric article. In that case a metallic mold or a moldlined with a metallic sheet will provide the metallic surface which willboth be determinative of the shape of the molded polymeric article andlead to the formation of the surface layer desired. The use of ametallic lining will lead to avoiding any loss of material from the moldand hence any change in the configuration thereof.

The surface layer of the metallized polymer composition according to theinvention, which contains the metal element A and the metal element B,is strongly bonded to the polymeric material. The thickness of thesurface layer may range from 0.01 to 100 microns, preferably from 0.1 tomicrons, depending on the process parameters.

Alternatively, the surface layer of the polymeric article may bethickened by further deposition of metal. Since the surface layer formedis electrically conductive it may serve as a preplating in aelectrodeposition process. Other, more cumbersome, methods may also beapplied. Thus, any metal may be deposited upon the surface layer ifreinforcement or functionalization of the surface is the primary object.However, if enhancement of the conductivity is envisaged, it ispreferred that use should be made of copper. Electrodeposited copperlayers were found to display a strong bond to the surface layer formedaccording to the invention.

The scope of the invention permits many advantageous uses of the presentprocesses. All fields of application of plated plastics or the formationof laminates may benefit from the simplicity and convenience of thepresent processes. The process of the invention may be beneficiallyused, for example, in the manufacture of printed circuit boards, forelectromagnetic interference shielding purposes, in the manufacture ofmembrane switches, for the decorative or functional coating of polymericarticles, for providing wear resistance to polymeric surfaces, for themanufacture of magnetic tapes or discs, anti-static mats or conductivefibers, in the production of capacitors, in the production of barrierpolymers, in the production of laminates and in the manufacture of tapesor discs of optical storage.

The surface layers obtained in the process of the invention show aninherent electrical conductivity which is sufficiently high forelectromagnetic interference shielding purposes. In the manufacture of ahousing for an electronic device an intimate mixture of acrylonitrilebutadiene styrene polymeric material, antimony oxide and trichloroacetic acid ester is injected into a mold lined with metallic copper.During molding a conductive antimony and copper containing surface layerof the polymeric material is formed at the contact face with the copperlining, providing a conductive coating of the polymeric article uponrelease from the mold. Generally, this surface layer will be overcoatedwith a paint for decoration and protection.

In the manufacture of printed circuit boards epoxy resin impregenatedsubstrate boards may be pressed onto stannous chloride coated copperfoils, resulting in a conductive surface layer being formed on thesubstrate board. Common semi-additive printed-circuit processingtechniques may then be used to provide a high-conductivity coppercircuit pattern.

In the manufacture of membrane switches, a paste comprising a mixture ofpolymeric binder and metallic copper powder coated with antimonytrichloride may be applied to a substrate in accordance with aparticularly derived circuit pattern. Heating will cause both the curingof the binder and the formation of an antimony-containing coating aroundeach copper particle, so that antimony coatings of adjacent copperparticles will coalesce with reduction in the resistivity of the circuitpattern obtained.

The outer surface of the metallic layer deposited on a plastic surface,by the present process, becomes well adhered to a new plastic surfaceunder the normal laminating conditions known to those familiar in theart. The new plastic surface may or may not be of the same compositionor structure as the initial plastic substrate on which the metallizationprocess was carried out. The laminating of different plastic materialsthrough sandwich layer of metallic composition laid down by the processdescribed herein, leads to strengthening and reinforcement of plasticlaminates and enables overcoming incompatibility hindrances associatedwith the blending and laminating of structurally diverse polymers.

The invention will further be illustrated by the following non-limitingexamples.

EXAMPLES Example 1

Cycolac T 10,000 ABS (Trademark) (an ABS polymer of 10,000 molecularweight supplied by Borg Warner) granules (93.9 g) were compounded with6.0 g of antimony trichloride (ex. BDH Ltd GPR grade) and 0.1 g ofcalcium stearate (employed as a lubricant) by milling on a two-roll mill(170° C. front roll, 165° C. back roll) for 5 minutes after gelation.

The milled sheet (1.0-1.2 mm thickness) was cut into 18.5 g. portionswhich were separately compression molded at 240° C. (2 minutes contacttime, 5 minutes at 6.15 MPa and 2 minutes at 6.15 MPa while cooled) incontact with a copper-berrylium (98:2) foil to yield a blue-orangemetallic coating on the portions of sheet which were easily separatedfrom the foil upon the release of pressure.

Example 2

100 g of cycolac T 10,000 ABS granules were milled with 0.1 g of calciumstearate, on a two-roll mill (front roll 160° C.) for 5 minutes aftergelation. The milled polymer was preformed into 9 cm×9 cm×0.16 cm sheetsby compression molding in a suitable mold at 170° C.

A 9 cm ×9 xm×0.0125 cm copper-berrylium alloy (98 Cu/2 Be) foil wasdegreased and mounted on a plate and a solution of antimony trichloridein dichloromethane sprayed onto the foil ensuring the uniform depositionof 0.35 g of antimony chloride on the foil surface.

The sprayed alloy foil was placed on a compression mold such that itscoated surface was in contact with a surface of the preformed ABS sheet.The polymer in the mold was subjected to hot compression (170° C., 6.15MPa) followed by cooling. The mold was opened and the ABS sheet found tobe coated with a metallic layer which remained adhered to the polymerafter separating away the copper-berryliium alloy foil. The weight ofthe ABS sheet was found to have increased by 2.22%, at the end of themetallization step.

Example 3

Cycolac T 10,000 ABS granules were pre-formed into 9 cm×9 cm×0.16 cmsheets as in Example 2.

A 9 cm×9 cm×0.0125 cm copper-berrylium alloy (98 Cu/2 Be) foil wasdegreased and mounted on a plate and a solution of antimony trichloridein acetone carrying a suspension of ABS powder (DSM, MST powder) wassprayed onto the foil.

The sprayed foil was placed over the pre-formed ABS sheet in acompression mold ensuring that the coated surface was in contact withthe polymer surface. The polymer was subjected to hot compression as inExample 2.

The ABS sheet was found to be metallized on its surface adjacent to theseparated alloy foil and the metallic coating was remarkably smooth anduniform.

Example 4

91.55 g of cycolac T 10,000 ABs granules were compounded with 2.0 g ofbismuth trioxide, 6.0 g of methyltrichlorobutyrate, 0.3 g of distearylthiodipropionate, 0.15 g of Irganox 1076 and 0.1 g of calcium stearateas for Example 1.

Upon compression molding in contact with a copper-berrylium foil as inExample 1, a blue-orange metallic coating was formed on the ABS surfaceadjacent to the contact foil.

Example 5

91.55 g of cycolac T 10,000 ABS granules were compounded with 4.0 g ofstannous oxide, 6.0 g of methyl trichlorobutyrate, 0.3 g of distearylthiodipropionate, 0.15 g of Irganox 1076 and 0.1 g of calcium stearateas for example 1.

Upon compression molding as in Example 1, a grey metallic coating wasformed on the ABS surface.

Example 6

A 9 cm×9 cm×0.15 cm sheet of cycolac T 10,000 ABS polymer was placednext to an anhydrous stannous chloride sprayed copper-berrylium foil andcompression molded for 20 minutes at 240° C. (6.15 MPa) to yield ametallic coating on the polymer surface.

Example 7

90 g of cellulose acetate (Dexel crystal×1915, Trademark) was compoundedwith 10 g of antimony tris (trichlorobutyrate) in a Brabender mixer at160° C. for 5 minutes after gelation.

30 g of the compounded composition was compression molded at 225° C. asin Example 1, to yield a metallic coating on the polymer surface.

Example 8

100 g of PVC (Corvic S 110/17, Trademark) powder was compounded with 30g of dioctyl phthalate and 1.0 g of a common barium-zinc stabilizer andmilled at 160° C. for 5 minutes.

A copper-berrylium alloy foil was sprayed with a solution of antimonytrichloride in dichloromethane and a 14.0 g portion of the milled sheetcut and placed in a compression mold, over the coated foil surface.

The polymer was compression molded at 175° C. (6 minutes contact time, 3minutes at 6.15 MPa) and cooled under 6.15 MPa to yield a metalliccoating on the surface of the polymer sheet.

Example 9

Pre-formed polycarbonate sheets (15 cm×15 cm×0.1 cm) were purchased fromGoodfellow, Cambridge, England and cut into 14 g pieces measuring 9 cm×9cm×0.1 cm.

A copper-berrylium alloy foil was mounted on a plate and sprayed with asolution of antimony trichloride in dichloromethane.

A polycarbonate piece (14 g) was placed at the bottom of a compressionmold chamber and the coated alloy foil positioned on top of the polymerensuring contact between the polymer and antimony trichloride coatedsurface. The mold was warmed to 170° C. and after a 6 minute contacttime to cause polymer gelation, a pressure of 6.15 MPa was applied for 3minutes. Upon cooling and opening the mold the outer surface of thepolycarbonate sheet was covered with a metallic layer which separatedeasily from the copper-berrylium foil.

Example 10

A 9 cm×9 cm×0.005 cm Melinex (Trademark) polyester film was placed nextto an antimony trichloride sprayed copper-berrylium foil and compressionmolded for 2 minutes at 190° C. (6.15 MPa) to yield a metallic coatingon the polymer surface.

Example 11

A 9 cm×9 cm×0.005 cm Kapton (Trademark) polyimide film was placed nextto an antimony trichloride sprayed copper-berrylium foil and compressionmolded for 5 minutes at 240° C. (6.15 MPa) to yield a metallic coatingon the polymer surface.

Example 12

A 9 cm×9 cm×0.155 cm copper-berrylium foil was sprayed with a solutionof antimony trichloride in diethyl ether and the coated foil was placedin a compression mold.

35 g of the epoxy molding compound, Polyset 217 (ex. DynachemCorporation, U.S.A., Trademark) was placed over the coated alloy foiland compression molded for 2 minutes at 150° C. under 6.15 MPa pressure.

After cooling the mold, the epoxy molding was found to have a metalliccoating on the surface that was adjacent to the alloy foil duringcompression.

Example 13

79.5 g of Hoechst S6600 (Trademark), high impact polystyrene, 10.0 g oftitanium dioxide (R900 Ti pure, Trademark), 0.5 g of calcium stearateand 10.0 g of antimony tris (trichlorobutyrate) were processed for 5minutes on a two-roll mill (front roll 210° C., back roll 200° C.).

A 8 cm×8 cm×0.20 cm piece of processed composition was compressionmolded allowing 3 minutes contact time and 6 minutes compression (6.15MPa) at 240° C. using two copper-berrylium alloy foils adjacent to thepolymer.

After cooling, the polymer was found to have a metallic coating on eachof the surfaces in contact with the alloy foil during compression.

Example 14

74.9 g. of polypropylene (Shell HY6100 N, Trademark), 10.0 g of titaniumdioxide (R900 Ti pure), 4.0 g of antimony trioxide, 10.0 g ofmethyltrichlorobutyrate, 0.5 g of calcium stearate, 0.2 g Irganox 1076and 0.4 g of distearylthiodipropionate were cross-blended on a two-rollmill (front roll 200° C., back roll 190° C.) for 5 minutes.

The blended composition was compression molded by allowing 3 minutescontact time prior to the application of 6.15 MPa pressure for 8 minutesat 240° C. after placing copper-berrylium alloy foils on each side ofthe polymer.

After cooling and foil separation, the polymer surfaces were found to becovered by an adherent metallic coating.

Examples 7-14 show that different polymeric materials, eitherthermoplastic or thermoset, may be metallized by the process of theinvention. The polymer compositions may contain processing aids such ascalcium stearate, and may optionally contain fillers, such as titaniumdioxide.

Example 15

A sheet of cycolac T 10,000 ABS polymer (10 cm×10 cm×0.2 cm) was sprayedwith a solution containing 5 g of antimony trichloride indichloromethane, followed by fine particle copper powder (3 um).

The sheet was transferred to an air circulating oven at 90° C. for 10minutes. The surface of the polymer sheet was found to have a uniformmetallic coating.

This example shows that elevated pressures are not essential in theprocess of the invention. However, elevated pressures do improve thesurface finish of the metallic coatings obtained.

Example 16

A 0.1 mm thick copper foil of 110 mm×150 mm was cleaned by theconsecutive steps of etching the oxide skin in a bath containing 100 mlof H₂ SO₄ per liter and 5 ml of H₂ O₂ for 30 seconds at roomtemperature, rinsing in water for 30 seconds, cathodic-alkalinedegreasing in a commercial degreasing bath for 3 min at 70° C. andthoroughly rinsing in cold water for 60 seconds. The wet copper foil wasplaced in an antimony plating bath containing 60 g of antimony trioxideper liter, 145 g of potassium citrate and 185 g of citric acid andcathodically antimonized at 50° C. and a current density of 1A/dm² for 2min. An antimony layer of an estimated thickness of about 2 microns wasthus electrodeposited onto the copper foil. The antimony coated copperfoil was subsequently rinsed with water and ethanol, dried andimmediately placed with its antimony face in contact onto a 2 mm thickABS sheet of 100 mm×100 mm (Metzoplast H, TiO₂ pigmented of MetzelerGmbH).

This assembly was placed between the two flat plates of a presspreheated to a temperature of 200° C. The pressure was graduallyincreased over 30 seconds to a total end load of 500 kg. The pressureand temperature were maintained for a further 90 seconds, whereupon itwas cooled to a temperature of about 50° C. over 5 min, and then thepressure was released and the assembly taken from the press.

Finally the ABS sheet carrying a Cu₂ layer was separated from the copperfoil.

In similar experiments thicker layers of antimony up to 10 um wereelectrodeposited onto the copper foil yielding thicker Cu₂ Sb coatingsof the ABS sheets. In many cases the Cu₂ Sb coated ABS sheet wasspontaneously released from the copper foil due to cooling tensions. Inall cases the contact surface of the copper foil after fission onlyshowed traces of residual Sb or Cu₂ Sb.

The metallic surface layer of the ABS sheet was subjected to X-raydiffraction analysis by means of a Philips PW 1700 powder diffractometer(reflection technique) using CuKx radiation and a quartz monochromator.The recorder spectrum was computer analyzed, compared with standardspectra of the JCPDS library and demonstrated to be that of thecopper-antimony intermetallic compound Cu₂ Sb.

Measurement of the adhesion of the Cu₂ Sb-layer to the ABS sheet wasattempted on an Elcometer adhesion tester, to which end cylindricaluminium dies were glued onto the fresh Cu₂ Sb surface of the coatedABS sheets. In 8 runs break tensions ranging from 150 to 413N/cm.sup. 2were observed, however, the break occurred at the glue faces or withinthe ABS sheet. In no case was fission observed at the Cu₂ Sb/ABSinterface.

Example 17

An antimony coated copper foil was prepared as in Example 16. It wasplaced upon at 100 mm×100 mm×1 mm sheet of polyethersulfon (Ultrason E2000 of BASF) previously dried at 130° C. under vacuum. After beingplaced in a press at 300° C. the assembly was subjected to a load of 500kg for 5 min at that temperature, whereupon it was cooled and thepressure released to obtain a polyethersulfon sheet having a surfacecoating of metallic appearance, which by X-ray diffraction was proven toconsist of Cu₂ Sb.

Example 18

The experiments of Examples 16 and 17 were repeated using otherpolymeric materials:

polyetheretherketone (Victrex PEEK of ICI); press conditions: 5 min at350° C.

polyetherimide (Ultem 1000 of General Electric); press conditions: 5 minat 350° C.

polyethyleneterephthalate; press conditions: 5 min at 250° C.

polybutyleneterephthalate; press conditions: 5 min at 250° C.

styrene acrylnitrile; press conditions: 5 min at 250° C.

In all cases metallized polymer sheets where obtained.

Example 19

Bonder steel plates were galvanized with sulfamate nickel to producenon-porous nickel coatings of about 10 microns thickness, which weresufficiently thick to prevent any exposure of free iron during thesubsequent experiments. The nickel coated Bonder plates, after rinsing,were antimonized in the bath and under the conditions described inExample 16. One Ni/Sb-coated plate was preheated for 1 hour at 300° C.and subsequently pressed onto an ABS sheet as described in Example 16. Ametallized ABS sheet was obtained, of which the surface layer was shownby X-ray diffraction to comprise the intermetallic compounds NiSb andNiSb₂.

The other Ni/Sb-coated plates were not preheated, but immediatelypressed onto sheets of polyethersulfon, polyetheretherketone andpolyetherimide as described before, at temperatures of 325, 350 and 350°C. respectively. In all cases intermetallic compound coatings wereformed on the polymer sheet, comprising NiSb and/or NiSb₂.

No iron was detected in the intermetallic compound layers.

Example 20

A zinc plate of 100 mm×100 mm×1 mm was antimonized in the bath describedin Example 16. Although the electroplating appeared to be suboptimal,local areas of antimony coating on the zinc plate could be obtained,which after pressing onto ABS at 250° C. produced an intermetalliccompound coating comprising SbZn and smaller amounts of Sb₃ Zn₄.

Example 21

An indium foil of 100 mm×15 mm×1 mm was antimonized as before. In viewof the melting point of indium of 156° C. the coated foil was pressedonto an ABS sheet at a temperature of 150° C. The surface layer of themetallized ABS sheet comprised the intermetallic compound InSb.

Example 22

A cu₂ Sb coated ABS sheet obtained as described in Example 16 waselectroplated at room temperature and at a current density of 1A/dm² ina CuSo₄ bath. The deposited copper layer showed an excellent adhesion tothe Cu₂ Sb surface layer of the ABS sheet.

Example 23

Various pastes emboding the present invention were madeup, applied as acoating to a polyester film and then cured. A summary of the samplesprepared is as follows:

    ______________________________________                                                  Sample No.                                                          Ingredients (g)                                                                           1        2     3        4   5                                     ______________________________________                                              Cu Powder 4        4   4        4   4                                         Urethane  5        5   5        5   5                                         SbCl.sub.3                                                                              2        3   4        5   6                                   (a)   Butanone  2        3   5        3   3                                   (b)   T Butanone                                                                              3        6   10       6   8                                   ______________________________________                                    

The Butanone and T Butanone were employed as solvents. There were twosamples corresponding to each sample number, each sample employing oneof the solvents.

The results obtained were as follows:

    ______________________________________                                                Paste                                                                 Results spreadability                                                                              Lumpiness  Conductivity                                  ______________________________________                                        1     (a)   good         slightly slight                                            (b)   good         slightly slight                                      2     (a)   good         slightly moderate                                          (b)   good         slightly moderate                                    3     (a)   bad          Very lumpy                                                                             high                                              (b)   bad          lumpy    high                                        4     (a)   poor         slightly high                                              (b)   good         slightly high                                        5     (a)   poor         lumpy    high                                              (b)   poor         lumpy    high                                        ______________________________________                                    

The above results indicate that although there was a degree of variationin the ease of applying the coating, the quality of the coating and itsconductivity, the invention was to varying degrees effective in allinstances. Conductivity did appear to decrease somewhat after a certaintime.

Example 24

A series of tests were carried out to determine the adhesive strength onpolymers of the intermetallic compound surface layers of the presentinvention as compared to surface layers of prior art compositionscomprising copper on polymer substrates prepared by prior art processes.

An Elcometer was used to measure the adhesive strength. An aluminum"dolly" was cemented to the metallized surfaces to be tested by means ofan epoxy resin, the metallized film was cut through around the cementeddolly and the dolly finally attached to the Elcometer which is aprecalibrated device which measures the force required to physically ripthe metallized film from the substrate.

The two prior art samples prepared were electroless plated copper on ABSpolymer and copper electrodeposited on epoxy.

The five samples prepared of the compositions of the present inventionwere Cu-Sb bulk mixed on ABS which was prepared as described in Example1, Cu-Sb via coated foil on both ABS and epoxy which was prepared as inExample 2 and CuSb using Cu powder on both ABS and epoxy which wasprepared as in Example 15.

The results of the tests were as follows:

    ______________________________________                                                          Adhesion Strength                                                             (Neutons/cm.sub.2)                                          Metal Layer         ABS    epoxy                                              ______________________________________                                        Electroless plated copper                                                                         412                                                       edc copper                 441                                                Cu--Sb bulk mixed   510                                                       Cu--Sb via coated foil                                                                            480    314                                                Cu--Sb using Cu--powder                                                                           461    451                                                ______________________________________                                    

The above results indicate that the adhesive strength of the metallicsurface layers of the present invention is at least comparable to thatof the prior art coatings. When the relative ease and simplicity of theprocess of the invention is taken into account it clearly would be theprocess of choice over the processes of the prior art.

We claim:
 1. A process for preparing a metallized polymer compositioncomprising reacting a compound or mixture of compounds containing apositive valent metal element A selected from the group consisting oftin, arsenic, antimony and bismuth with a metallic source of a metalelement B selected from the group consisting of iron, cobalt, nickel,copper, zinc, gallium, ruthenium, rhodium, palladium, silver, cadmium,and indium at the surface of said polymer composition at a temperatureand pressure appropriate for obtaining a surface layer on the polymercomposition comprising an intermetallic combination containing both themetal element A and the metal element B.
 2. The process of claim 1wherein a support surface is provided which comprises said metal elementB.
 3. The process of claim 2, wherein said reaction is effected withsaid surface of said polymer composition being pressed onto said supportsurface with said compound or mixture of compounds being between saidsurface of said polymer composition and said support surface.
 4. Theprocess of claim 3, wherein said compound or mixture of compounds isfirst applied to said surface of said polymer composition.
 5. Theprocess of claim 3, wherein said compound or mixture of compounds isfirst applied to said support surface.
 6. The process of claim 3,wherein said compound or mixture of compounds is first applied to bothsaid surface of said polymer composition and said support surface. 7.The process of claim 2, wherein said support surface is of a shape thatwill determine the shape of the surface of the polymer composition to bemetallized, said polymer composition being pressed onto said supportsurface to effect molding of said polymer composition during saidreaction.
 8. The process of claim 2, wherein said compound or mixture ofcompounds containing a positively valent metal element A is incorporatedinto said polymer composition prior to said reaction.
 9. The process ofclaim 2, wherein said support surface comprises a mold on the surface ofwhich a foil of the metal element B is placed.
 10. The process claim 1wherein said compound or mixture of compounds comprises a hydride,halide, sulfide, phosphide or carboxylate of the metal element A or itsprecursors.
 11. The process of claim 1 wherein at least part of saidsurface layer is further plated by deposition of additional metal.
 12. Aprocess for preparing a metallized polymer composition comprisingbringing into contact at least one layer of zero-valent antimony and atleast one layer of a metal element B selected from the group consistingof iron, cobalt, nickel, copper, zinc, gallium, ruthenium, rhodium,palladium, silver, cadmium and indium with a polymer or prepolymercomposition at a temperature and pressure appropriate for obtaining apolymer composition having a surface layer comprising an intermetalliccompound of antimony and the metal element B.
 13. The process of claim12 wherein said layer of metal element B constitutes the surface layerof a body consisting essentially of said metal element B.
 14. Theprocess of claim 12 wherein said layer of metal element B is a layerdeposited upon an inert release substrate.
 15. The process of claim 12wherein said metallizing conditions include a pressure in the range offrom about 100 kPa to about 10 MPa to effect said contact.
 16. Theprocess of claim 12 wherein said metallizing conditions include atemperature range of from ambient temperature to about 600° C.
 17. Theprocess of claim 16 wherein said metallizing conditions include atemperature of from about 125° to about 375° C.
 18. A process of claim12 wherein at least part of said surface layer is further plated bydeposition of additional metal.